Chemical Nomenclature

Chemical nomenclature is the term given to the naming of compounds. Chemists use specific rules and "conventions" to name different compounds. This section is designed to help you review some of those rules and conventions.

When forming compounds, it is important to know something about the way atoms will react with each other. One of the most important manners in which atoms and/or molecules react with each other is the oxidation/reduction reaction. Oxidation/Reduction reactions are the processes of losing and gaining electrons respectively. Just remember, "LEO the lion says GER:" Lose Electrons Oxidation, Gain Electrons Reduction. Oxidation numbers are assigned to atoms and compounds as a way to tell scientists where the electrons are in a reaction. It is often referred to as the "charge" on the atom or compound. The oxidation number is assigned according to a standard set of rules. They are as follows:

An atom of a pure element has an oxidation number of zero.

For single atoms in an ion, their oxidation number is equal to their charge.

Fluorine is always -1 in compounds.

Cl, Br, and I are always -1 in compounds except when they are combined with O or F.

H is normally +1 and O is normally -2.

The oxidation number of a compound is equal to the sum of the oxidation numbers for each atom in the compound.

Knowing the oxidation number of a compound is very important when discussing ionic compounds. Ionic compounds are combinations of positive and negative ions. They are generally formed when nonmetals and metals bond. To determine which substance is formed, we must use the charges of the ions involved. To make a neutral molecule, the positive charge of the cation (positively-charged ion) must equal the negative charge of the anion (negatively-charged ion). In order to create a neutral charged molecule, you must combine the atoms in certain proportions. Scientists use subscripts to identify how many of each atom makes up the molecule. For example, when combining magnesium and nitrogen we know that the magnesium ion has a "+2" charge and the nitrogen ion has a "-3" charge. To cancel these charges, we must have three magnesium atoms for every two nitrogen atoms:

3Mg2+ + 2N3- --> Mg3N2

Knowledge of the charges of ions is crucial to knowing the formulas of the compounds formed.

In naming ions, it is important to consider "isomers." Isomers are compounds with the same molecular formula, but different arrangements of atoms.
Thus, it is important to include some signal within the name of the ion that identifies which arrangement you are talking about. There are three
main types of classification, geometric, optical and structural isomers.

Geometric isomers refers to which side of the ion atoms lie. The prefixes used to distinguish geometric isomers are cis meaning
substituents lie on the same side of the ion and trans meaning they lie on opposite sides. Below is a diagram to help you remember.

Optical isomers differ in the arrangement of four groups around a chiral carbon. These two isomers are differentiated as L and D.

Structural isomers differentiate between the placement of two chlorine atoms around a hexagonal carbon ring. These three isomers are identified as
o,m, and p. Once again we have given you a few clues to help your memory.

Binary acids (H plus a nonmetal element) are acids that dissociate into hydrogen atoms and anions in water. Acids that only release one hydrogen atom are known as monoprotic. Those acids that release more than one hydrogen atom are called polyproticacids. When naming these binary acids, you merely add "hydro-" (denoting the presence of a hydrogen atom) to the beginning and "-ic acid" to the end of the anion name.

Examples:
HCl = hydrochloric acid
HBr = hydrobromic acid

Ternary acids (also called oxoacids, are formed by hydrogen plus another element plus oxygen) are based on the name of the anion.
In this case, the -ate, and -ite suffixes for the anion are replaced with -ic and -ous respectively. The new
anion name is then followed by the word "acid." The chart below depicts the changes in nomenclature.

A detailed treatise on naming organic compounds is beyond the scope of these materials, but some basics are presented. The wise chemistry student should
consider memorizing the prefixes of the first ten organic compounds:

Number of Carbons

Prefix

1

meth-

2

eth-

3

prop-

4

but-

5

pent-

6

hex-

7

hept-

8

oct-

9

non-

10

dec-

There are four basic types of organic hydrocarbons, those chemicals with only carbon and hydrogen:

Single bonds (alkane): suffix is "ane", formula CnH2n+2

Double bonds (alkene): suffix is "ene", formula CnH2n

Triple bonds (alkyne): suffix is "yne", formula CnH2n-2

Cyclic compounds: use prefix "cyclo"

So, for example, an organic compound with the formula "C6H14" would be recognized as an alkane with six carbons, so its name is "hexane".